Associate county Medical Examiner Leszek Chrostowski, left, uses defense attorney Brian Gonzalez’s neck to show how marks on Stephen Tomlinson’s throat could have been produced.

TAMPA — Authorities got it all wrong when they charged Joshua Rosa with first-degree murder, his defense attorney says. Rosa, 22, had "reasonable, plausible" explanations for being in Logan Gate Park when he found the body of his 13-year-old neighbor on Dec. 8, 2005.

But at Rosa's trial Wednesday, a medical examiner debunked some of his claims.

Rosa had told deputies that he lost his keys while jogging in the Carrollwood subdivision park. He returned with a flashlight to look for them and came upon the body of Stephen Tomlinson, with whom he had played video games and attended church.

Rosa said he heard Stephen gurgle, so he tried to help the teen by puncturing his throat with a key to open an airway. He also said he wiped blood from Stephen's mouth and nose with white gloves he had with him.

Investigators found Rosa's keys by Stephen's body. Was there any evidence, a prosecutor asked the medical examiner Wednesday, that someone used a key to puncture the teen's neck?

"No," said Dr. Leszek Chrostowski.

The doctor also said blood on Stephen's face was not smeared.

The 121-pound, 5-foot-4 teen died of manual strangulation sometime the night of Dec. 8, the doctor said, though he couldn't pinpoint exactly when.

Stephen had bruises on his body that indicated a struggle, Chrostowski said. The teen's death likely occurred from more than a single choke hold, he said.

Rosa, a former church leader with no prior criminal record, studied martial arts and practiced karate moves with Stephen in the Tomlinson's driveway, Stephen's father has previously said.

Florida Department of Law Enforcement crime lab analysts told jurors that Stephen's blood was found on Rosa's shoe, jogging pants, hands and white gloves. DNA from both Rosa and Stephen — skin cells, not blood — was found on fingernail clippers Rosa had in his pocket.

Investigators think Rosa may have used the clippers to try to remove evidence; he has made no such admissions.

Gonzalez suggested that DNA transferred from the gloves to the clippers because they were in the same pocket.

Amy Rockhold, an analyst, said that was possible but not likely. She saw a lot of blood on the gloves, none on the clippers.

Colleen Jenkins can be reached at cjenkins@sptimes.com or (813) 226-3337.